This invention pertains to computer based methods for determining whether certain frontal or angular crash situations in a vehicle require activation of a safety device. More specifically, this invention pertains to the use of two acceleration sensors, one in the passenger compartment and one centrally located at the front of the vehicle in such a method. The method involves the continuous selective use of velocity and displacement values from the two sensors in at least three different modes of crash situations to determine whether a safety device, such as a passenger compartment air bag, is to be activated and, if so, how it is to be activated.
Safety devices for the protection of the operator and passengers of automotive vehicles have been in use for many years. Many safety features function in a crash situation without external activation. Seat reinforcement, seat headrests, and passenger compartment padding are examples of such safety items. Other safety devices such as supplemental inflatable restraints, popularly known as air bags, require external activation when a crash event is apparently occurring.
Air bags comprise an inflatable bag, an electrically actuated igniter and a gas generator. Each bag is folded and stored with its igniter and gas generator in the steering wheel pad, instrument panel, door panel or body pillar. Air bags also require a collision detection system that determines when the bags should be deployed and signals the ignition of one or more charges (or stages) of the gas generator. Current air bag, and other passive passenger protection systems, rely on acceleration sensors (detecting abrupt vehicle deceleration) and a micro-processor based controller. An acceleration sensor is a device that continually senses accelerative forces and converts them to electrical signals. The controller continually receives acceleration signals from each sensor and processes them to determine whether a crash, situation is occurring that requires air bag deployment.
The content of such a crash detection system for safety device actuation usually depends upon the method or algorithm used by the controller for assessing crash severity. Most systems rely on an acceleration sensor placed in the passenger compartment, close to the center of gravity of the vehicle. This sensor is often put under the passenger seat as part of a sensing and diagnostic module (SDM) of the vehicle crash sensing system. In addition, some systems place one or more accelerometers at the center or sides of the radiator cross-tie-bar to detect vehicle front-end deceleration indicative of a crash. These front-end accelerometers have been called electrical frontal sensors, EFS. The crash detection controller receives signals from the acceleration sensor(s) and evaluates them in a preprogrammed manner to determine whether air bag deployment is necessary. The program may also determine the degree of deployment, e.g., one or two inflation stages, of the bag.
The algorithms of crash sensing controllers have involved increasing degrees of complexity. Acceleration values from a single sensor (e.g., the SDM sensor) have simply been compared with a pre-determined threshold acceleration value as a test for device deployment. Values from more than one sensor location have been used in the crash sensing practices. Acceleration values have been integrated over time to yield crush velocities, and further integrated to yield crush displacement values. Further, the derivative of acceleration values have been determined as xe2x80x9cjerkxe2x80x9d values Such velocity and displacement values, and jerk values, have also been compared with respective pre-determined threshold values as a more selective basis for achieving timely air bag. Also, acceleration data has been used in combination with seat occupancy information and seat belt usage.
There are variants in vehicle front-end crash modes and, of course, there can be considerable variation in the severity of a crash depending upon the structure and mass of a vehicle and its velocity at the onset of a crash. With respect to front-end crash modes, a vehicle may crash head-on with another vehicle (a full frontal crash mode) or with a narrower fixed object such as a pole. Front-end crashes of a vehicle with other vehicles often occur in an angular mode between head-on (zero degree) and a side-ways crash (ninety degrees). A further distinction is often made between an angular crash with a rigid or non-yielding object and an offset deformable barrier (OBD mode).
Actual vehicular crash testing reveals different patterns of front end and passenger compartment crush velocities and displacements associated with different crash modes. In fact, considerable crash testing of a vehicle has been required to provide the substantial database of threshold values of jerk, acceleration, velocity and/or displacement over a crash period for use by a crash-sensing controller. Such data must be compiled from suitably instrumented test vehicles over the relevant duration of each test crash period. Depending upon the nature and severity of a crash, an airbag deployment decision may be made by the controller process at any time during a period of from about 15 milliseconds (ms) to 70 ms or 100 ms or so from the onset of the crash.
It would be desirable to obtain a discriminative and robust crash sensing algorithm that could utilize suitable crash simulation models as a basis for establishing threshold values of, e.g., velocity and displacement at two or more acceleration sensor locations in a vehicle. Crash simulation models may be based, for example, on a suitable Finite Element Analysis (FEA). As stated, such threshold values must be obtained over a period of up to about 70 to 100 ms from the recognition of a crash event and stored in the memory of the controller. Accordingly, it is an object of this invention to provide a method of activating an air bag or other crash-responsive safety device that can utilize velocity and displacement values obtained from a suitable crash model. It is a further object of this invention to provide such a method that utilizes velocity and displacement values from two sensors, one located in the passenger compartment and one located centrally at the front of the vehicle. It is a still further object of this invention to provide an airbag activation method that utilizes a consideration of three or more distinct vehicle crash modes in use of time integrated acceleration sensor data.
This invention provides a vehicle crash sensing system which better discriminates severe crash events that require actuation of safety devices from minor crash incidents that do not require such actuation. This is accomplished by use of two acceleration sensors and an associated signal processing algorithm in a microprocessor. The crash sensing algorithm is composed of at least three parallel assessment branches or modules for detecting different crash modes, each of which uses only current velocity and displacement measures calculated by integrating the acceleration data recorded from the two vehicle mounted accelerometers.
In accordance with the invention a centrally located, front end acceleration sensor is employed together with a sensor in the passenger compartment. For example, the front end acceleration sensor, EFS, may be mounted at the center of the radiator cross-tie-bar in the engine compartment of the vehicle for sensing the acceleration of the tie-bar. The vehicle is also provided with an accelerometer in the passenger compartment, such as a location underneath the passenger seat as a part of a sensing and diagnostic module (SDM) of the vehicle crash sensing system. The vehicle crash sensing system detects and discriminates severe crash events from minor crash incidents by signals derived from the front end acceleration sensor and the SDM acceleration sensor. Such derived signals are used in the signal processing algorithm of this invention which is implemented in the control program within the microcomputer of the crash sensing system.
In a preferred embodiment of the invention, the control method uses sensor data in a manner to determine air bag inflation needs in each of a full frontal crash mode, a pole mode and an angular crash mode. Additional representative crash modes could be used but these three are sufficient and exemplified. When activated by predetermined threshold acceleration values from both sensors indicative of a possible crash, the subject method proceeds by continually integrating acceleration data from the two sensors to obtain corresponding velocity values for each sensor location over a period of up to 100 milliseconds or so. Further the acceleration data from the tie bar sensor is used to continually calculate two displacement values, one based on actual acceleration values and one based on corresponding absolute values of acceleration.
Thus, the acceleration data recorded at the central radiator tie bar (EFS) sensor (Ac) and the SDM sensor (As) are filtered and digitized. The respective signals are integrated over several milliseconds to calculate Vs, Vcm, Sc and Scad. Here Vs denotes the velocity at the SDM sensor; Vcm and Sc denote the maximum velocity and the actual displacement at the central front-end sensor location; and Scad denotes a displacement measure based on the absolute acceleration values at the central front-end sensor location, as explained in detail later. Following activation of the process, the acceleration and velocity values for the passenger compartment sensor are continually associated with times, to, and acceleration, velocity and displacement values for the front end sensor associated with times, tor, and stored in the memory of the vehicle""s crash controller.
These velocity and displacement values are selectively used in a series of three parallel crash mode calculations and logical tests, namely a full frontal mode module, angle mode module, and a pole mode module. Preferably, each crash mode module has two sub-modules, i.e. the 1st and 2nd stage airbag deployment modules.
In accordance with the invention, the sensing algorithm uses the digitized acceleration signals, As and Ac, from both the SDM accelerometer and the EFS accelerometer to enable (or initiate) operation of the crash sensing method of this invention. The control method determines whether the acceleration, As, at the passenger compartment location is equal to or greater than a predetermined acceleration threshold which, for example, may be set at 2 g""s (g being the acceration due to gravity). At the same time the acceleration, Ac, of the front-end sensor is compared with a larger threshold acceleration of, e.g., 8 to 12 g, suitable for the specific vehicle. If both As and Ac are not greater than the respective enable thresholds, the program loops back to monitoring the input. This controller cycle is repeated every millisecond or so.
At such time as a value of As is obtained that is greater than its enable threshold, the program initiates the system clock, to, and starts calculations of SDM velocity and displacement. If Ac does not then surpass its enable threshold within a predetermined time period, e.g., 10 to 20 ms, from the SDM enabling, the program is reset and loops back to monitoring inputs. But if a timely value of Ac is obtained that is greater than its enable threshold, the system clock, tor, is initiated and the calculation of the measures at the EFS is started. Conversely, if Ac exceeds its enable threshold first, the program initiates the system clock, tor, and starts the calculation of velocities and displacements at the front sensor. If, As does not surpass its enable threshold within a predetermined period, e.g., 10 to 20 ms, after the front sensor enabling, the program resets and loops back to monitoring the acceleration inputs. But if a timely value of As is obtained that is greater than its enable threshold, the system clock, to, is initiated and the calculation of the measures at the SDM location is started.
The sensing system is reset in the case of minor crash incidents by a reset module which determines whether the velocity measure, Vs, is equal to or greater than a predetermined threshold. If Vs is not equal to or greater than the reset threshold, the program loops back to monitoring the input. If Vs is greater than the threshold, the program advances to detailed crash analysis.
Once the crash severity determining method is enabled, the velocities and displacements are calculated and entered into the three branching program modules; the frontal crash mode module, the angle crash mode module and the pole crash mode module. The module for which the 1st stage thresholds are first exceeded initiates the deployment of the airbag. Then its corresponding 2nd stage sub-module determines the severity of the crash by comparing the measures with another set of thresholds. The other modes are ignored after a first stage deployment decision has been made.
In the frontal mode, first stage assessment, velocity values are used. It has been observed that the velocity measures, Vs and Vcm are generally very high for severe frontal full-barrier-like impact events. Accordingly, they are used in the method of this invention to determine whether or not to trigger the deployment of the first stage airbag inflator for this type of impact events. If, and only if, both velocity measures for an event are equal to or greater than a set of velocity thresholds, predetermined by experiment or calculation for the vehicle at the corresponding time (to or tor) in the crash sequence, the program will send a triggering signal out to ignite the first stage air bag inflation. In a typical vehicle, a full frontal mode situation will be detected and the air bag inflated within 10-25 ms of impact.
If first stage air bag inflation has been commanded through the frontal mode program module, the frontal mode, second stage determination is made. The velocity measure, Vcm, is used alone to determine whether or not to trigger the deployment of the second stage airbag inflator for this type of frontal full-barrier-like impact events.
In parallel with its analysis of the frontal mode-first stage the controller is also analyzing the angle crash mode, first stage and the pole crash mode, first stage. As stated, results from any crash mode analysis can trigger first stage air bag inflation.
The angle crash mode-first stage analysis is characterized by both relatively high speed and low speed impacts either of which may require airbag inflation. It has been found that a combination of the passenger compartment velocity measure, Vs, and the front end velocity, Vcm are generally high to very high for severe angle like events. For lower speed events, a combination of high values of front end velocity, Vcm, and a front end displacement, Scad, are considered. As stated, the Scad displacement value is based on the absolute value of Ac as will be shown in detail below. Accordingly, it is preferred to use these two combinations as alternatives in the angle mode to determine whether or not to trigger the deployment of the first stage airbag inflator for this type of impact events. In assessing the second stage of the angle mode, a suitably high front end displacement, Sc, is used as the basis for determining the triggering of the second stage airbag inflator.
In the pole mode-first stage a combination of velocity of the SDM sensor, Vs, and maximum velocity, Vcm, at the central front end sensor are used in assessing the severity of a pole crash mode type event. It will be recognized that these same values are used in the frontal mode first stage analysis. However, the time based threshold velocity values for this mode differ substantially from those for the frontal mode reflecting the differences in the crash characteristics of the two modes.
Values of Vcm are used in the second stage pole mode analysis.
A critical feature of a crash severity determination method is the availability of suitable threshold velocity and displacement values over a period of up to 100 ms for each acceleration sensor and device activation. These threshold values may be based on physical crash test data for the specific vehicle, or crash model data, or a combination of test data and modeling.
Other objects and advantages of the invention will become apparent from a detailed description of illustrated embodiments which follows.